1. Field of the Invention
The present invention concerns an operating method for a magnetic resonance system. The present invention furthermore concerns a data medium with a computer program stored on the data medium, a control and evaluation device for a magnetic resonance system and a magnetic resonance system.
2. Description of the Prior Art
Magnetic resonance systems are generally known and are normally operated as follows:
An RF excitation coil emits an excitation pulse such that nuclei in an examination subject are excited to emit magnetic resonance signals. The magnetic resonance signals emitted from the examination subject are acquired and transmitted to an evaluation device. The evaluation device corrects the transmitted signals using correction signals and uses the corrected signals for reconstruction of an image of the examination subject. The correction of the signals by the evaluation device is required in order to compensate phase errors that otherwise would lead to artifacts in the reconstruction of the image of the examination subject.
The magnetic resonance signals emitted by the examination subject can alternatively be acquired with a whole-body antenna or with one or more local coils. The present invention concerns the case of the magnetic resonance signals being acquired by local coils.
It is naturally possible for each local coil to directly supply the magnetic resonance signal acquired by it to the evaluation device. In this case, each acquired magnetic resonance signal is transmitted to the evaluation device via its own transfer channel. This operating mode is known as array operation of local coils.
It is also known for the local coils to supply the magnetic resonance signals acquired by them to a combination unit that is normally arranged in proximity to the local coils. The combination unit determines from the magnetic resonance signals a number of intermediate signals and (depending on the setting of the combination unit by an operator of the magnetic resonance system) transmits at least one intermediate signal, or possibly a number of intermediate signals, to the evaluation device. Each transmitted intermediate signal is transmitted to the evaluation device via its own transfer channel. This operating mode is known as matrix operation.
Conventionally, the correction signals are determined separately for each transfer channel. The determination normally ensues using signals acquired previously and transmitted via the respective transfer channel. For magnetic resonance signals acquired by a whole-body antenna, this procedure leads to good results. In array operation and in matrix operation of the local coils, however, it can lead to artifacts in the reconstruction (known as ghost images) which can significantly impair the quality of the reconstruction.